Phosphorylation of initiation factors is thought to be an important control mechanism in protein translation. A protein kinase has been described in rabbit reticulocytes which phosphorylates the small (alpha) subunit of eIF-2, the eukaryotic initiation factor which forms a ternary complex with GTP and met-tRNAf in one of the first steps of protein translation initiation. This kinase, called the hemecontrolled repressor (HCR), is activated only in the absence of hemin and is a potent inhibitor of globin synthesis. Investigations from our laboratory, described in this proposal, have shown that an analogous protein kinase exists in human reticulocytes. The rabbit and human eIF-2 alpha kinase differ in that the rabbit kinase may be activated in post-ribosomal supernatant whereas the human kinase may only be activated in ribosome-replete preparations, either intact reticulocytes or lysates. Analogously to the rabbit system, the human kinase cannot be activated in the presence of added hemin. In this study we will further purify and characterize human eIF-2 alpha kinase. Initial purification of this kinase indicates that it copurifies with globin synthesis inhibition activity. This inhibition mechanism may be important in the hypochromic anemias associated with heme deficiency. Therefore, we also propose to study peripheral reticulocytes and bone marrow erythroid precursors from patients with disorders associated with heme deficiency to determine if eIf-2 alpha is present in an activated form. These studies should clarify the mechanism of the hypochromic anemia associated with iron deficiency, the sideroblastic anemias, certain cases of preleukemia, and lead poisoning.